Infrared (IR) staring sensors are well known in the prior art for obtaining data in the IR spectrum. Typically, devices that use sensors include an optical train that is centered on an optical axis. The optical train receives the optical rays through an aperture, and then directs the incoming IR optical rays onto a focal plane array (FPA) for further processing and display by other components of the device. One of the disadvantages of these devices, however, is that during operation, a portion of the incoming IR radiation actually reflects off the focal plane array, passes back through the optical device and leaves the device through the aperture as an IR emission signal. This phenomenon is known as retro-reflectivity.
It is extremely desirable that the retro-reflectivity for the device be minimized. This is because a remote laser interrogator can use the retro-reflection to locate and even target the sensor and it associated weapons system (along with the operators nearby). Stated differently, it is desirable to minimize retro-reflectivity of the device, so that the IR staring sensor is undetectable during operation of the device.
In view of the above, it is an object of the present invention to provide an IR sensor with a decentered field lens for minimizes retro-reflectivity. Another object of the present invention to provide an IR sensor with a decentered field lens that minimizes retro-reflectivity via refraction of incoming IR optical rays. It is another object of the present invention to provide an IR sensor with a decentered field lens that minimizes retro-reflectivity over two or more distinct ranges of IR wavelengths. Another object of the present invention is to provide an IR sensor with a decentered lens that is made of a non-linear optical material to provide protection from laser damage. A further object of the present invention is to provide an IR sensor that cannot be detected with a remote sensor during its operation. Another object of the present invention is to provide an IR sensor that is relatively easy to manufacture in a cost-effective manner.